Abstract: Separation of impure surface water layer, separation of mixture of impurities and water and method for implementation of discharging impurities separated, according to which local water level lowering required for flowing impure surface water layer through overflow spillway is performed in conformity with the Bernoulli formula by suction effect produced and maintained by increasing flow rate, while separation taking place in the same step is carried out by the transient decrease of flow rate, then by change of direction. By turbulent-free inflow without decrease of rate really excellent scraping efficiency can be achieved.